This invention relates to starting and operating apparatus for low-pressure, positive-column discharge devices of the fluorescent type and, more particularly, to such apparatus for operating three, four, five or six fluorescent lamps.
The fluorescent lamp ballast art is highly developed and the most commonly used ballast, particularly for recessed fixture commerical applicatons, is the two-lamp series-sequence ballast which is generally referred to as a two-lamp rapid-start ballast. For purposes of comparison, a general sketch of this ballast is shown in FIG. 1 of the present application. Such a ballast is described in greater detail in U.S. Pat. No. 2,796,554, dated June 18, 1957.
Another type of ballast which has been used in the past is the so-called lead-lag circuit which is shown in FIG. 2 for purposes of comparison. Other types of commerical ballasts are of the so-called instant-start type such as described in U.S. Pat. No. 2,558,293, dated June 26, 1951. Ballasts designed according to this instant start principle can be either of the lead-lag type of the series-sequence type.
The patent and other literature also contains references to many hundreds of different types of ballast designs, the vast majority of which have never been commercial. A patent representative of such ballast designs, which is of some interest with respect to the present design, is U.S. Pat. No. 2,424,505, dated July 2, 1947, wherein a ballast inductor and capacitor operate at near resonance and the same inductor and a second capacitor are partially resonant at the line frequency, to ballast two individual lamps. In U.S. Pat. No. 2,719,937, dated Oct. 4, 1955, is disclosed a lead-lag type of circuit for operating two lamps in conjunction with separate heating transformers. In U.S. Pat. No. 3,754,160, dated Aug. 21, 1973, one ballast operates four individual lamps in series-parallel arrangement. In U.S. Pat. No. 3,875,459, dated Apr. 1, 1975, is disclosed a solid-state starter circuit used with a preheat fluorescent lamp.